Large reversible magnetocaloric effect in RNi compounds

In an attempt to identify novel magnetic refrigerant materials, we have studied the magnetic and magnetocaloric properties in RNi compounds with R = Gd, Ho and Er. GdNi is a simple ferromagnet with a collinear structure in contrast to HoNi and ErNi, in which the moments of rare earth sublattice are arranged non-collinearly. The magnetic ordering temperatures are observed to be 69 K, 36.5 K and 10 K for GdNi, HoNi and ErNi, respectively. The maximum values of magnetocaloric effect are found to be 17 J kg^-1 K^-1, 15 J kg^-1 K^-1 and 29 J kg^-1 K^-1 for Gd, Ho and Er, respectively, for an applied field of 50 kOe. The relative cooling power has been calculated to be 527 J kg^-1 K^-1, 780 J kg^-1 K^-1 and 510 J kg^-1 K^-1 for GdNi, HoNi and ErNi. These values compare well with those of many potential materials whose magnetic transitions are in the same range as in the present case.